This invention relates to telephone systems and, in particular, to telephone systems which include central office switches adapted to provide advanced intelligent network (AIN) operations and services.
One method of providing services in an advanced intelligent network is to utilize service nodes or intelligent peripherals, e.g., telephone stations, private branch exchanges, voice mail systems, etc., which have various degrees of intelligence and which communicate with the central office switch using message based digital signalling protocols. In many of these telephone systems, the interface between a service node and the central office switch is an "integrated services digital network" (ISDN) interface. ISDN interfaces have two basic common configurations.
In a first configuration, the ISDN interface includes two channels commonly referred to as the "B" channels (usually 64 Kb/sec) which carry voice and/or user data information. This first configuration of ISDN interface also includes a third channel commonly referred as the "D" channel (16 Kb/sec) which carries telephone network access and/or control signalling information. ISDN interfaces of this first configuration are referred to as "basic rate" or 2B+D ISDN interfaces.
A second configuration of the ISDN interface is similar to the first configuration, but the interface includes 23 "B" channels for voice and data (usually at 64 Kb/sec), in addition to the one "D" channel for access and/or control signalling (in this case, also at 64 Kb/sec). This second configuration of the ISDN interface is referred to as a "primary rate" or 23B+D ISDN interface.
Both configurations of ISDN interface and their associated procedures support the invocation of supplementary services (i.e., requests above and beyond call establishment) through a protocol called the "Common Element" procedures. This allows requests to be associated with a current call (e.g., call transfer), as well as requests that are not directly associated with a current call. This particular latter subset of the Common Element procedures is called non-call associated signalling. A particular example might be non-call associated signalling which is used to indicate to a subscriber that a message is waiting (i.e., signalling used to turn on a message waiting indicator on a telephone station at a subscriber location).
Non-called associated signalling is conveyed in a Facility Information Element of the ISDN protocol. This information element is usually carried in a non-call associated message (e.g., the ISDN REGISTER message) which is identifiable to the central office switch. This message is first processed in the switch as defined by the ISDN Common Element procedures and then further processed in the switch as indicated and required by the specific service (e.g., a message waiting indication service).
A more thorough description of the specifications for ISDN interfaces used by the regional Bell telephone companies appears in documents known as Technical References published by Bellcore. These Technical References are based in part on relevant international standards established for ISDN signalling (namely Recommendations Q.931 and Q.932) and the relevant national standards. The Bellcore documents are identified by so called "TR numbers" and for ISDN interfaces and their associated central office requirements, the following Technical References have been developed: TR-NWT-01268, ISDN Primary Rate Interface Call Control Switching and Signalling Requirements for Class II Equipment; TR-TSY-00268, ISDN Access Call Control Switching and Signalling Requirements, Issue 3; and TR-NWT-000864, Common Element Procedures for Service Control, Issue 1. An example of a specific service that utilizes the existing Common Element procedures can be found in TR-NWT-000866, ISDN Message Service. The aforesaid TRs and the aforesaid international and national standards are known in the telephone system art and their teachings are incorporated herein by reference.
In telephone systems utilizing conventional and ISDN interfaces, the central office switches have also been further adapted to include advanced intelligence network (AIN) capabilities so that the switches can provide additional services to the telephone subscribers of the system. Central office switches adapted in this manner are generally referred to as "service switching points". The additional services that can be provided by such service switching points include display based delivery of the calling party's name, audio delivery of the calling party's name, automatic rerouting of calls based on network failure, etc.
In conjunction with providing these additional services, a central office switch or service switching point must, in many cases, communicate with an intelligent computer or so-called "service control point" to obtain information necessary to complete the service. Thus, for example, when the central office switch encounters a call to a called subscriber who subscribes to a service for display based delivery of a calling party's name (sometimes referred to as "Calling Name Delivery"), the central office switch will suspend its normal call set-up processing to query a service control point having a data base which correlates directory numbers with subscriber names. The query by the central office switch will request the service control point to search its data base for the subscriber name having the calling directory number.
Once this calling subscriber information is obtained from the service control point, the central office switch will complete the call set-up procedure. When the call is established, the central office switch will then provide the calling subscriber name to the called subscriber utilizing analog transmission technologies and thus complete its Calling Name Delivery service.
The interface between a central office switch and its service control points in a telephone system is collectively known as "SS7". The SS7 interface is internal to the telephone system and only accessible through certain types of telephony related equipment (referred to as "network elements"). The procedures and protocols of SS7 are subdivided into functional groupings as identified by protocol layers and each network element processes certain protocol layers. The signalling between an AIN switch and a service control point largely involves the Transaction Capabilities Application Part of SS7 more commonly known as TCAP and to a lesser extent, the Signalling Connection Control Part, more commonly known as SCCP.
Routing for the SS7 TCAP messages is usually provided by a signalling transfer point which communicates with the central office switch and the various service control points. The routing functions are defined in the Signalling Connection Control Part of SS7. The central office switch formulates a signalling connection control part message for carrying each TCAP message. The signalling connection control part message also includes origination (calling party) address information and destination (called party) address information.
When a switch sends a TCAP message, the switch`s origination or calling party address information in the corresponding signalling connection control part message contains a so-called "signalling point code" which uniquely identifies the switch. The destination or calling party address information also includes a sub-system number which identifies a particular application process of the switch associated with processing the TCAP message. If AIN processes are involved, the sub-system number is usually a generic AIN identifier which corresponds to one of the generic AIN versions (i.e., AIN Release 0, AIN Release 0.1 or potentially AIN Preliminary Release 0.2).
The destination or called party address information in the signalling connection control part message contains either a signalling point code and sub-system number which identify the service control point and the required application processing or a "global title" identifier and a "Translation type" identifier. The latter two identifiers permit the signalling point code and the sub-system number of the destination service control point to be derived via a translation table at the signalling transfer point.
When the signalling transfer point receives a signalling connection control part message, the signalling transfer point routes the message to the destination service control point based upon the signalling point code and sub-system number sent in the message or derived from the translation table at the signalling transfer point. Upon receipt of the routed message, the destination service control point recognizes the type of processing that is to be carried out from the sub-system number in the called party information.
After completing its specific processing as determined by the TCAP message contents, the service control point may formulate an acknowledgement TCAP message. This TCAP message is transmitted in a signalling connection control part message to the signalling transfer point. The signalling transfer point routes the message back to the central office switch which is identified in the message by its signalling point code in the called party information. Upon receipt of the signalling connection control part message, the switch retrieves the TCAP message to obtain the information provided by the service control point to complete the AIN service.
A more extensive description of the specifications for SS7 interfaces, including the signal connection control part messages and TCAP messages, is provided in Bellcore TR-NWT-000246, Signalling System Number 7, Issue 2. Also, the AIN Release 0.1 and the Preliminary AIN Release 0.2 are described in detail in Bellcore Technical Requirements TR-NWT-001285, TR-NWT 001284 and Technical Advisories TA-NWT-1299, TA-NWT-1298 and TA-NWT-001129. The aforesaid Bellcore TRs and TAs are also incorporated herein by reference and likewise are known in the telephone system art.
In the above-described non-call associated signalling schemes defined in TCAP in SS7 and in the Common Element Procedures of ISDN, each non-call associated message includes a "component" which indicates the status of the operation. The following components are used: (a) Invoke; (b) Return Result; (c) Return Error; and (d) Reject.
The Invoke component in a message indicates that the identified operation in the message is being requested. The Return Result component indicates that the associated operation is being positively acknowledged and the Return Result may contain information necessary in providing the acknowledgment (i.e. the information requested). The Return Error component indicates that the associated operation is being negatively acknowledged, i.e., that the entity that received the message was not able to carry out the requested operation. The Return Error component may contain information as to the reasons why the operation could not be carried out. The Reject component indicates that the entity that received the message was not able to understand the nature of the requested operation at all.
As above-indicated, a central office switch communicates with its service control points based on the aforesaid TCAP SS7 messages, while it communicates with its service nodes based on the aforesaid ISDN messages. The central office switch does not permit the service control points to be accessed by the service nodes (or any other subscriber or customer premises equipment) or vice-versa, i.e., the service nodes to be accessed by the service control points, via directory dialing or any other means. This is a disadvantage since access of the service nodes and the service control points to each other in a telephone system may be desirable to permit AIN processes to be directly requested or effected.
It is, therefore, an object of the present invention to provide a telephone system in which the service nodes and the service control points of the system can access one another in an efficient and cost effective manner.
It is a further object of the present invention to provide a telephone system meeting the above objective in which ISDN interfaces with ISDN messages are used between the service node and the central office switch and SS7 interfaces with TCAP messages are used between the central office switch and the service control points.
It is yet a further object of the present invention to provide a telephone system meeting the above objectives and which utilizes existing procedures to the greatest extent possible.
It is still a further object of the present invention to provide a service node, central office switch and service control point for a telephone system meeting the above objectives.